Heat pads for pets are known. One example is the Snugglesafe® heat pad that is disc-shaped, contains a non-toxic gel, and can be heated in a microwave. (The Snugglesafe® heat pad is supplied by Lenric C21 Ltd of Unit 10, Thorgate Road, Littlehampton, BN17 7LU, United Kingdom).
A fleece cover is typically provided to prevent the pet from coming into direct contact with the heat pad.
Existing heat pads such as the Snugglesafe® are not particularly satisfactory for use in hutches or enclosures. Because they are typically flat, the heat pad must be placed on the surface of the bedding (e.g., straw, hay or wood shavings), or buried within in. When the heat pad is removed, the bedding can be stuck to the fleece cover and it must be cleaned after being exposed to pet droppings, urine etc.